Chemical pesticides and fungicides are the most commonly used control agents for forest insect pests and fungal diseases. In excess of 350 billion pounds of these agents are used annually in the United States to control pests and diseases in forestry, agriculture, and residential areas. Broad spectrum insecticides and fungicides have adverse impacts not only on their target organisms but also on beneficial insects and fungi and, consequently, on the entire ecosystem. In addition, chemical residues may cause health problems among the human population.
Interest in biological insect and fungal control agents is growing as a consequence of concerns regarding chemical pesticide use. A number of bacteria synthesize antifungal compounds and over 1500 microorganism and microbial products have been identified that are insecticidal. Generally, natural control agents have little adverse ecological impact due to their specificity for the target host. Long term environmental hazards and health concerns are not a factor with biological control agents because chemical residues are not present. Unfortunately, biological control agents suffer from several disadvantages in comparison to chemical pesticides, including cost of production, efficacy, and stability.
One particularly troublesome plant pest is the gypsy moth Lymantria dispar. The gypsy moth was first imported from Europe into North America near Boston in 1869. Since then, the area of gypsy moth infestation has increased to include almost the entire New England area, New York, Delaware, Maryland, New Jersey, Pennsylvania, Virginia, West Virginia, Ohio, and Michigan. (McFadden, et al., Forest Insect Guilds: Patterns of Interaction with Host Trees, Y. N. Baranchikov, et al. pp. 172-186. US Department of Agriculture, For. Serv. Gen. Tech. Rep. NE-153, Radnor, Pa., 1989.) Several chemical insecticides have been used for gypsy moth control. DDT is one of the most effective chemical insecticides used against gypsy moths.
Knowledge of the environmental impacts of DDT and other chemical insecticides has caused all industry shift to the use of agents such as Dimilin and Bacillus thuringiensis (Bt) for gypsy moth control. The Lymantria dispar nuclear polyhedrosis virus (LdNPV), which is pathogenic to Lymantria dispar (gypsy moth), is also used as a biocontrol agent. LdNPV has the significant advantage over other control agents of specificity for the gypsy moth. Consequently, LdNPV is the agent of choice for all areas and particularly for use in environmentally sensitive areas. However, LdNPV is not used extensively for gypsy moth control because of high production costs and low efficacy. One particular problem with LdNPV propagation in cell culture is the propensity of the virus to mutate into a form that produces fewer polyhedra (FP mutants).
For gypsy moth virus production to be competitive, means of reducing production costs must be devised. One approach is the development of insect cell lines that produce high amounts of polyhedra. Lynn et al., (Appl. Envron. Microbiol., 55, 1049-1051, 1989) have developed a fat-body cell line that produces greater amounts of polyhedra than other gypsy moth cell lines.
What is needed in the art of gypsy moth control is an improved strain of LdNPV capable of enhanced production.